Cryogenic flask arrangement



June 25, 1968 P. J. WALSH ETAL 3,389,566

CRYOGENI C FLASK ARRANGEMENT Filed Jan. 30, 1967 Pare-z (Tn 44:, 1 47 06 /t fiyeo,

United States Patent 3,389,566 CRYOGENIC FLASK ARRANGEMENT Peter J. Walsh, Los Augcles, Calif., and Patrick N. Byrd,

North Palm Beach, Fla.; said Walsh assignor to Hughes Aircraft Company, Culver City, Calif., a corporation of Delaware Filed Jan. 30, 1967, Ser. No. 612,450 4 Claims. (Cl. 62-45) ABSTRACT OF THE DISCLQSURE A flask formed of thermally insulating material is provided with a central cavitied cooling finger to receive liquid cryogenic fluid from a remote source via a transfer line. The arrangement structurally includes a centering tube partially disposed within the finger and formed of a material having a relatively high thermal conductivity. The opposite end of the centering tube projects from the arrangement and is in thermal contact with ambient whereby some heat is transferred into the cavitied finger to maintain a temperature profile therein at the proper level, avoid over-cooling and yet minimize the loss of cryogenic fluid due to vaporization.

The invention relates to a cryogenic flask arrangement and has particular utility in devices which cool a heat load at cryogenic temperature ranges and maintain the load at such temperature level over extended periods of time.

Recently developed detecting arrangements which are sensitive to electromagnetic Wave radiation on broad spectral bands require, for efficient operation and accurate wave detection, that they be maintained at extremely low temperatures, for example, 80 Kelvin and below. At such temperature levels the devices, such as infrared detectors, efficiently respond to sensed electromagnetic wave radiation and provide output signals that accurately reflect the radiation received. Many modes have been proposed to maintain the devices at such extremely low temperature levels, most common being to encapsulate the device in a flask or container, sometimes called a Dewar, which is in effect an insulated vessel and to deliver to the encapsulated detector a cryogenic fluid which, in its liquefied state, exists at the desired cryogenic temperature level. In the usual circumstance the cryogenic fluid is liquefied by an appropriate machine such as a refrigerator which is remotely located from the flask-encapsulated device. Delivery of the liquefied cryogen from its point of storage or manufacture to the Dewar is frequently accomplished by a mode known in the art as Liedenfrost transfer and which is described in US. Patent 2,996,893, dated Aug. 22, 1961. Briefly, this mode of transfer and delivery utilizes a transfer tube having a stream of cryogen in droplet form moving therethrough. The tube, per se, is essentially at ambient temperature and above the liquefaction temperature of the cryogen. Small droplets of liquid from its source are entrained in the moving gas within the transfer tube, and the surface of each drop boils, i.e., vaporizes from its liquid to gaseous state and forms a thermally insulating gaseous envelope around each droplets through the tube entrained in the moving gas. Thus, of the droplet and makes possible the transfer of the droplets through the tube entrained in the moving gas. Thus, the cryogen liquid is moved from its source to point of utilization without employing heavy or bulky thermal insulation for the transfer tube.

characteristically, the Dewar is provided with a hollow finger having an entrance at one end aspect of the flask, said finger extending into the flask and providing a cryogen storage chamber adjacent the device location. The

transfer line for the liquid cryogen is telescopically received in the finger and projects therein whereby the droplets of cryogen liquid are deposited in the chamber adjacent the devices and there form a pool of liquid cryogen the vaporization of which supplies the cooling or refrigerating effect to maintain the device at appropriate temperature. Characteristically, the encapsulating flasks and the inner fingers thereof are formed of glass or ceramic material which have a low coefficient of heat conductivity.

In many systems currently using detecting devices, such as infrared detectors, the service application requires that the detector operate over extended time periods. Continuous operation for several days or more is not an unusual requirement. A difficulty has developed in that during extended operative periods the continuous delivery of liquid cryogen to the flask-defined finger has created a condition of over-cooling which in effect means that the device and adjacent areas of the flask are brought to a temperature below the optimum temperature level and as a result the efficient operation of the device is impaired. In prior art systems when this condition occurred it has been the practice merely to shut down this entire system, halt delivery of cryogen to the flask-defined chamber until such time as the temperature profile of the flask and encapsulated device reached the proper level. Such a practice, of course, in essence, defeated the operation of the entire system. The problem thus presented is to provide an arrangement wherein a proper temperature profile may be created and maintained at the device and Dewar during long term system operation.

It is therefore a primary object of the invention to provide a thermally insulating arrangement having a chambier-defining internal finger to receive the liquid cryogen, said finger having telescopically received. therein a centering tube of relatively high thermally conductive material, said tube being thermally coupled to ambient to provide a heat sink within the finger above cryogenic temperature level and thereby maintain a desired temperature profile in the chamber and at the adjacent device.

The above and other features and advantages of the invention will become apparent by reference to the following specification and to the related drawings wherein:

FIGURE 1 is a central, vertical, cross-sectional view partly in elevation of an encapsulating flask incorporating the invention; and

FIG. 2 is a detailed view of a centering tube incorporated in the structure of FIG. 1.

Referring to the drawings, the numeral 10 generally indicates an encapsulating flask of the type described above. This flask or Dewar may sometimes be referred to as an insulating envelope. As shown at 12, at the broken cross-sectional central section of the drawing, the flask 10 may be constructed of any thermally insulating material having a low coefficient of thermal conduction such as glass, ceramic material or the like. The flask 10 internally defines an elongated cavity or finger 14 projecting therein which includes a chamber 16 at its inner end adapted to receive liquid cryogen as hereinafter described. At the end of the chamber 16, metallic wool 18 may be deposited to entrap delivered cryogenic fluid and, due to surface tension, maintain the cryogenic droplets at the related end of chamber 16.

The Dewar 10 may further include a mounting element 20 which in the preferred embodiment may be cylindrical in form, said mounting element 20 receiving the adjacent end of the flask 10 as illustrated. The flask 10 may besecured to the element 20 by filling the cylindrical element 20 with an appropriate potting compound, such as is shown at 22., which not only provides a mode of connection but also acts as an insulating material.

In the detailed View of FIG. 2, a centering tube is indicated generally at 26. In a preferred embodiment the tube comprises an elongated hollow cylinder 28 having a radially expanded section 30 at one end thereof which is integrally formed with an annular flange 32. The tube may be chamiered into a funnel shape as at 34 at one end thereof. It is noted that the tube is formed of material having relatively good thermal conduction characteristics, and at cryogenic temperature ranges in which the arrangement is most useful, copper is an appropriate material.

Returning to the arrangement of FIG. 1, it will be noted that the centering tube 26 is telescopically received within the finger 14 with the enlarged segment 30 projecting outwardly therefrom and received within the potting material 22. The tube 26, however, is free to move and may be inserted or removed from the finger 14 and material 22. The cylinder 20 is provided with a metallic cover 40 substantially closing one end thereof. The cover 40 is provided with a central opening to receive enlarged segment 30 and shoulder abut the projecting annular flange 32 of the tube 26. The cover 40 may be internally threaded as at 42 to threadably receive a locking member 43. The cap 44 may be provided with a central opening 48 through which projects cryogenic delivery tube 50, the latter having a terminating pipe 52 projecting into the centering tube 26. The cap 40 supports the tube 50 and is further provided with a flange 45 interposed between locking member 43 and flange 32. Thus, the threaded-mounted locking member 43 secures the entire arrangement.

Considering the above structural description, it will be apparent that the thermally conductive centering tube 26 is clamped in heat transfer relation with the cover 40 by virtue of the physical contact between the tube flange 32, cover 40, cap 44, and the lOCking member 43. In effect, the tube 26 is thermally coupled to ambient.

As noted above, when in service, liquid cryogen is delivered to chamber 16 as liquid droplets moving through delivery tube 50 and terminal pipe 52. The drop- 'lets are then directed to the chamber 16. The tube 26, being thermally coupled to ambient, as above described, maintains a temperature level above the temperature level of the delivered liquid cryogen and as the cryogen strikes the tube 2.6 it partially vaporizes and each droplet froms a thermally insulating gaseous envelope as it moves down the tube 26 for deposit in chamber 16.

During operation, heat is received from ambient, thermally transferred through the cap 40, locking member 44, flange 32, and to the centering tube 26. In this mode a proper temperature profile is maintained in the chamber 16 and the adjacent structure of encapsulating flask 10,

overcooling is prevented and a minimum amount of the refrigerating effect of the liquid cryogen is lost.

The invention is by way of illustration and not limitation and may be modified in many respects within the spirit and scope thereof.

What is claimed is:

1. In a detecting device cryogenic mounting arrangement,

an insulating envelope defining a cavitied finger therein,

a heat transfer tube partially disposed in the cavitied finger,

one end of said tube being in heat trans-fer relation with ambient,

said finger including a chamber at one end to receive and store cryogenic liquid,

said chamber being spaced from the end of the tube,

a cryogenic liquid transfer line communicating with the cavitied finger and the tube,

said transfer line being partially telescoped into said tubewhereby a substantial area of the tube is exposed to the liquid between the termination of the line and the chamber,

and closure means for the cavitied finger and the tube comprising a cap physically abutting the tube.

2. A detecting device cryogenic mounting arrangement according to claim 1,

wherein said cap is provided with an opening to accommodate the entrance of said transfer line to the tube.

3. A detecting device cryogenic mounting arrangement according to claim 2,

wherein said heat transfer tube includes an annular flange abutting said closure cap and in conductive thermal transfer relation therewith.

4. A detecting device cryogenic mounting arrangement according to claim 3, and including,

a locking element operative to clamp said flange to said closure cap.

References Cited UNITED STATES PATENTS 3,055,191 9/1962 Dennis 62514 X 3,064,451 11/ 1962 Skinner 62-514 X 3,306,075 2/1967 CoWans 62514 3,315,478 4/1967 Walsh et al 625l4 LLOYD L. KING, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,389,566 June 25, 1968 Peter J. Walsh et al.

It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, lines 62 and 63, "droplets through the tube entrained in the moving gas. Thus," should read droplet. This insulating envelope inhibits further vaporization Signed and sealed this 27th day of January 1970.

(SEAL) Atte st:

Edward M. Fletcher, 11'. WILLIAM E.

Attesting Officer Commissioner of Patents 

